1. Field of the Invention
The present invention relates to a vehicle headlamp, and more particularly relates to a vehicle headlamp having a mechanism that allows the headlamp to be used in several beam modes using a discharge tube having a single light emitting section.
2. Description of the Related Art
At present, so-called projector-type or multireflector-type headlamps dominate the vehicle headlamp market, which concentrate light with high precision by arranging a reflecting mirror around a halogen lamp (iodine bulb) which is close to a point source with power consumption of 35 to 60 watts and high efficiency of about 20 lumens/watt. Two standards are set for the projector-type headlamps: PE (polyellipsoid) and DE (three-dimensional ellipsoid) type. The multireflector-type headlamps use a MS (multisurface) type.
FIG. 6 is an external view of a conventional vehicle headlamp 1. FIGS. 7A to 7C are sectional views of the vehicle headlamp 1, in which FIG. 7A shows a case in which a halogen lamp 2 is used as a light source and FIG. 7B shows a case in which a discharge tube 3, such as a xenon lamp, is used as a light source, and FIG. 7C is an enlarged view of a filament section of the halogen lamp 2. The headlamp 1 in FIG. 7A is a so-called projector-type or multireflector-type headlamp, in which two light emitting sections (filament) 52 and 50 of the halogen lamp (iodine bulb) 2 which is close to a point source with power consumption of 35 to 60 watts and high efficiency of about 20 lumens/watt, that is, a high-beam light emitting section 52 and a low-beam light emitting section 50 covered with a shade 51 are arranged in line in the direction of arrow Z (back and forth in a state in which the headlamp 1 is mounted to the vehicle), around which a reflecting mirror 55 is disposed, thereby concentrating light with high precision.
In the headlamp 1 in FIG. 7A, light beams that are emitted from the two high-beam light emitting section 52 and low-beam light emitting section 50 covered with the shade 51 are sent toward the reflecting mirror 55 in the direction of X (laterally in a state in which the headlamp 1 is mounted to the vehicle) and in the direction of Y (vertically in a state in which the headlamp 1 is mounted to the vehicle), respectively, and are reflected in the direction of Z by the reflecting mirror 55.
The halogen lamp 2 used in the headlamp 1 lights up by applying a voltage as low as 12V or 24V, thus requiring no special insulation and having an average operating time of 400 hours. Several types of specifications, called H-1 type, HB-1 type, H-4 type, HB-4 type, HB-5 type, H-7 type and so on, are set in shape, for each of which the shapes and sizes of a base mounting section (lamp holder) on the side of illuminating apparatus and a flange base on the side of the halogen lamp are standardized.
Conventionally, the low beam and high beam in the headlamp using the halogen lamp were switched by selecting two dedicated halogen lamps which are arranged at approximately the center of the reflecting mirror divided for high beam and low beam; however, recently, the high-beam light emitting sections 52 and the low-beam light emitting section 50 covered with a shade are provided side by side in one halogen lamp, as in the H-4 type shown in FIG. 7A, and are selected for illumination. More specifically, for high beam emission, only the high-beam light emitting section 52 is lit up and, for low beam emission, only the low-beam light emitting section 50 covered with the shade 51 is lit up to block off light on the side of the shade 51 and alter the reflection by the reflecting mirror, thus controlling light distribution.
On the other hand, in the halogen lamp 2 used in the headlamp 1, as shown in FIG. 7C, the relative position of the high-beam light emitting section 52 and the low-beam light emitting section 50 covered with a shade is deviated from each other. Specifically, the high-beam light emitting section 52 and the low-beam light emitting section 50 are separated, at the center point, by L2 (about 6.5 mm) in the Z direction and by L1 (about 1.2 mm) in the Y direction. Consequently, the reflecting surface of the reflecting mirror 55 is set to reflect light in a predetermined direction at each position of the high-beam light emitting section 52 and the low-beam light emitting section 50. More specifically, the high-beam light emitting section 52 and the low-beam light emitting section 50 are selectively lit up, wherein, when the high-beam light emitting section 52 is lit up, light beams IH1 and IH2 are reflected by the reflecting mirror 55 to irradiate a distance, and when the low-beam light emitting section 50 is lit up, only a light beam IL1 is reflected by the reflecting mirror 55 to become a downward light beam and irradiate a short distance.
There is also provided a discharge tube, such as a xenon lamp, as a light source taking the place of the halogen lamp 2. In this discharge tube, although the voltage applied at initial lighting is as high as about 20,000V, highly efficient 100±15% lumens/watt is provided, thus providing luminous flux twice as large as that of the halogen lamp. Also, the power consumption is only about 35 W and the operating time is more than four times as long as that of the halogen lamp. Accordingly, it is the most suited to save energy and ideal for a vehicle headlamp. The headlamp, particularly, the vehicle headlamp must be constructed to switch low-beam and high-beam; however, it is structurally difficult for the present discharge tube 3 to include two light emitting sections in the lamp itself, as in the halogen lamp 2 of the H-4 type.
Also, there is a problem of spacing in that separate two discharge tubes are provided near the center of the reflecting mirror, as in the conventional type, and it is also difficult to construct the reflecting mirror. Furthermore, it is relatively expensive in cost. Accordingly, even if the conventional discharge tube 3 is arranged as in FIG. 7B, the conventional switching of low-beam and high-beam cannot be performed, so that when a light emitting section 53 of the discharge tube 3 is arranged at a position where the high-beam light emitting section 52 of the halogen lamp 2 is to be arranged, the light beams IH1 and IH2 are reflected by the reflecting mirror 55 to irradiate only a distance.
There is provided a headlamp disclosed in Japanese Unexamined Patent Application Publication No. 2001-35211, which solves the above problems. Such a headlamp has a structure including a drive unit K for sliding a shade 67 for shielding a light emitting section 65 of a discharge tube 64 disposed at a base 61 in the direction of arrow X along the axis Z of the discharge tube 64, as shown in FIGS. 8A and 8B. FIG. 8A is a front view showing the structure of the discharge tube 64 and the base according to an embodiment of the invention disclosed in the above-mentioned application in a low-beam mode and FIG. 8B is a front view of the same in a high-beam mode. A leg 67b of the shade 67 is connected through the base 61 to a moving iron 69 of a solenoid 68 secured to the back of the base 61 with a rod 66 and so on. The moving iron 69 is biased at all times by a spring 60, so that when the solenoid is inoperative, a shielding surface 67a of the shade 67 stands in the position of the light emitting section 65 to block off the light from the discharge tube 64 partly, thus providing low-beam light distribution. The coil of the solenoid 68 is energized to draw the moving iron 69 against the stress of the spring 60 and to slide the shade 67. When the shielding surface 67a gets out of position of the light emitting section 65 of the discharge tube 64, light is radiated from the light emitting section 65 in almost all directions to provide high-beam light distribution.
The above method, however, has the following problems: The high-beam light emitting section 52 and the low-beam light emitting section 50 are separated at the center point by L2 in the Z direction and by L1 in the Y direction, as described above. However, in the headlamp disclosed in Japanese Unexamined Patent Application Publication No. 2001-35211, the shade 67 for shielding the light emitting section 65 is only slid in the direction of arrow X along the axis Z of the discharge tube 64. Consequently, a light emitting section can only be placed at the position of one of the high-beam light emitting section 52 and the low-beam light emitting section 50.
On the other hand, the reflecting surface of the reflecting mirror 55 is shaped to reflect light in a predetermined direction at each position of the high-beam light emitting section 52 and low-beam light emitting section 50. Accordingly, the conventionally used reflecting mirror cannot be used but a special reflecting mirror is required to irradiate a predetermined position with light, thus increasing the cost for the headlamp. Also, the standard for vehicle parts is strictly decided; for example, the shape of the reflecting mirror is standardized, as mentioned above, in which the versatility of possible shapes, sizes, installation spaces thereof is low, thus being limited in design.
Also, in the headlamp disclosed in Japanese Unexamined Patent Application Publication No. 2001-35211, the moving iron 69 of the solenoid 68 is secured to the back of the base 61 with the rod 66 and so on. The moving iron 69 is biased at all times by the spring 60. Therefore, a mechanism for moving the light emitting section 65 of the discharge tube 64 or the shade 67 must be long, thus causing various limitations to enclose such a mechanism in the standardized reflecting mirror.